Pseudohyponatremia remains a problem for clinical laboratories. In this study, we analyzed the mechanisms, diagnosis, clinical consequences, and conditions associated with pseudohyponatremia, and future developments for its elimination. The two methods involved assess the serum sodium concentration ([Na]_S) using sodium ion-specific electrodes: (a) a direct ion-specific electrode (ISE), and (b) an indirect ISE. A direct ISE does not require dilution of a sample prior to its measurement, whereas an indirect ISE needs pre-measurement sample dilution. [Na]_S measurements using an indirect ISE are influenced by abnormal concentrations of serum proteins or lipids. Pseudohyponatremia occurs when the [Na]_S is measured with an indirect ISE and the serum solid content concentrations are elevated, resulting in reciprocal depressions in serum water and [Na]_S values. Pseudonormonatremia or pseudohypernatremia are encountered in hypoproteinemic patients who have a decreased plasma solids content. Three mechanisms are responsible for pseudohyponatremia: (a) a reduction in the [Na]_S due to lower serum water and sodium concentrations, the electrolyte exclusion effect; (b) an increase in the measured sample’s water concentration post-dilution to a greater extent when compared to normal serum, lowering the [Na] in this sample; (c) when serum hyperviscosity reduces serum delivery to the device that apportions serum and diluent. Patients with pseudohyponatremia and a normal [Na]_S do not develop water movement across cell membranes and clinical manifestations of hypotonic hyponatremia. Pseudohyponatremia does not require treatment to address the [Na]_S, making any inadvertent correction treatment potentially detrimental.

Background: There is conflicting information on current medical and surgical complications associated with high body mass index (BMI) after kidney transplantation. Methods: In a single-center observational study, we analyzed the 5-year outcomes of all consecutive primary kidney transplant recipients between 2010 and 2015 based on BMI at the time of transplant. Results: There were 1,467 patients included in this study, distributed in the following groups based on BMI: underweight (n = 32, 2.2%), normal (n = 407, 27.7%), overweight (n = 477, 32.5%), grade I obesity (n = 387, 26.4%), grade II obesity (n = 155, 10.6%), and grade III obesity (n = 9, 0.6%). Obesity was associated with an increased incidence of delayed graft function (p = 0.008), length of stay (LOS, p = 0.03), 30-day surgical re-exploration (p = 0.02), and hospital readmission (p < 0.0001). Obesity was also associated with higher 1-year serum creatinine (p = 0.03) and increased 5-year incidence of cardiac events (p < 0.0001) and congestive heart failure (p < 0.0001). Multivariable Cox regression analyses determined grade III obesity (HR = 5.84, 95% CI: 1.40–24.36, p = 0.01), LOS >4 days (HR = 1.94, 95% CI: 1.19–3.18, p = 0.008), hospital readmission (HR = 2.25, 95% CI: 1.20–4.22, p = 0.01), 1-year serum creatinine >1.5 (HR = 1.95, 95% CI: 1.20–3.18, p = 0.007), and proteinuria (UPC) >1 g/g (HR = 1.85, 95% CI: 1.06–3.24, p = 0.03) as independent predictors of death-censored graft failure. Conclusion: In the current era of renal transplant care, obesity is common, and high BMI remains associated with significant medical and surgical complications after transplant.